In various fields, such as medical care, foods, materials, and the like, conventionally, a technique for culturing cells has been used. In a cell culture, in most cases, formed are colonies in each of which cells are clustered. In a case where many cells are cultured, it is required to analyze images obtained by imaging colonies, to thereby automatically specify only necessary colonies.
In an image processing apparatus disclosed in WO 2011/010449 (Document 1), for example, a user designates a candidate for an iPS cell colony from a synthetic macro image which is a phase contrast microscope image of a culture vessel. By binarizing the synthetic macro image, a binarized colony image is obtained, and from the binarized colony image, a contour line of the designated cell colony is extracted. After that, it is determined whether each cell colony is an iPS cell or not from its feature value.
Also in a cell image analysis apparatus disclosed in Japanese Patent Application Laid Open Gazette No. 2011-24485 (Document 2), a boundary element of an object is extracted by using its luminance and/or luminance difference. At that time, in a case where parts of the boundary element are separated since the amount of variation in the luminance and/or luminance difference is small, the boundary elements which are away from each other at a distance not larger than a predetermined value are identified as those of the same object, and these boundary elements are connected with line segment elements.
In Document 1, since the cell colony which has a clear contour line and is clearly distinguished from the background is designated by the user, it is relatively easy to extract the contour line of the cell colony. In Document 2, though it is considered that there are breaks in the boundary line due to noises or the like, it is not assumed that there is a condition where the boundary is blurred and thickened. In a case where the boundary is blurred due to imaging blur or misfocus, the contour is apt to be wrongly detected.